1. Field of the Invention
The present invention relates to a lubrication mechanism for a wave gear device, and in particular to a lubrication mechanism for a wave gear device that prolongs the lubrication life.
2. Related Art
A typical wave gear device comprises a ring-shaped rigid internal gear, a flexible external gear that is shaped like a cup and is disposed on an inside of the rigid internal gear, and a wave generator for flexing the flexible external gear elliptically so that the flexible external gear engages the internal gear and moving engaging positions of the two gears in a circumferential direction. The number of teeth in the two gears usually differs by two, so that the engaging positions of the gears move in the circumferential direction and the two gears rotate relative to each other. Since the internal gear is fixed, rotating the wave generator at high speed using a high-speed rotational driving source, such as a motor, results in a rotational output of significantly reduced speed being obtained from the external gear.
The wave gear device has frictionally contacting parts to be lubricated that include the engaging toothed surfaces of the two gears, frictionally contacting parts of the external gear and the wave generator, frictionally contacting parts within the wave generator, and the like. Usually, the same type of lubricant is supplied to all of these parts.
The nature of the frictional contact at each of these lubricated parts differs, however, so that the desirable properties for the lubricants used at such lubricated parts also differ. With a conventional lubrication mechanism where the same type of lubricant is used to lubricate each lubricated part of a wave gear device, lubrication problems occur at some lubricated parts before others. This limits the lubrication life of the wave gear device as a whole.
The present invention has a main object of providing a lubrication mechanism for a wave gear device that can prolong the lubrication life of the wave gear device.
To achieve the above and other objects, the present invention is a lubrication mechanism for a wave gear device, the wave gear device including: a ring-shaped rigid internal gear; a ring-shaped flexible external gear; and a wave generator for flexing the external gear in a radial direction and has the external gear partially engage the internal gear, and for moving engaging parts of the internal gear and the external gear in a circumferential direction, the lubrication mechanism including: grease that fills toothed parts of the internal gear and the external gear; and a solid lubricant that is attached to frictionally contacting parts within the wave generator and to frictionally contacting parts of the external gear and the wave generator.
The grease should preferably have a base oil viscosity of 68 mm2/s (at 40xc2x0 C.) and a worked penetration (at 25xc2x0 C.) in a range of 220 to 295.
The solid lubricant should preferably be produced by mixing a grease with a resin and hardening the mixture by heating.
The solid lubricant may also be fixed to an inner circumferential surface of the external gear that contacts the wave generator.
Since the wave generator includes a rigid wave plug, a wave bearing that is fitted between an outer circumferential surface of the wave plug and an inner circumferential surface of the external gear, and a retainer for the wave bearing, the solid lubricant may be fixed to the retainer.
With the lubrication mechanism for a wave gear device according to the present invention, the frictionally contacting parts of the engaging toothed parts of the two gears are filled with grease that has a high base oil viscosity and favorable shear stability (i.e., a lubricant suited to these parts). Also, at the frictionally contacting parts on the inside of the wave generator and the frictionally contacting parts between the wave generator and the external gear, solid lubricant with low base oil viscosity and low deformation resistance (i.e., a different lubricant suited to these parts) is used. By doing so, the lubrication life can be prolonged without degrading the efficiency of the wave gear device.